This invention relates to toggling bistable devices and particularly to electromagnetic indicators for evidencing one of two conditions, such as a "set" or "reset" condition.
In many instances an apparatus must achieve and hold one or another condition in response to a brief signal. For example, a device may need to respond to a short electrical signal and then maintain that response to show whether a system is operating properly or improperly. For such purposes, it is common to use set-reset or "yes" or "no" indicators which retain their position despite cessation of the signal that actuated the indicator.
Many of these indicators and other bistable devices rely upon springs to move a armature into alternate positions and an electromagnetic force to move it between positions. These have been found undesirable for a number of reasons. A number of devices have been disclosed which accomplish results of this nature by biasing an armature in one or the other direction with a permanent magnet. In these types of devices, a winding energized by an indicating circuit induces a magnetic field which overcomes the biasing force of the permanent magnet and shifts the armature into another position where a permanent magnet holds the armature despite the cessation of the current in the field-inducing winding. The proximity of the armature to one of the permanent magnets compared to the distance from the other permanent magnet, assures retention of the armature into one of the two bistable conditions.
While such devices find use in some applications, they are complex, require heavy actuating currents, or are difficult to assemble.